Tuning device



Nov. 25, 1924. 1,516,947

L. J. BEINDORF TUNING DEVICE Filed Sept. 8, 1922 2 Sheets-Sheet lINVENTO/ L me@ Jem Off Bywwwo.

Nov. 25, 1924. 1,516,947

L. J. BENDORF TUNING DEVICE Filed Sept. 8, 1922 2 Sheets-Sheet 2 f6 1Bymf..

Afro/M578 .'Patented Nov. 25, 19214.

LUCIEN J. BEINDO'RF, OF CHICAGO, ILLINOIS.

TUNING Application illed September To all whom it may concern.'

Be it known that I, LUcmN J. BmNooiu` a citizen of the United States,and a resident of Chicago, in the county of Cook and State of Illinois,have invented a new and useful Improvement in Tuning Devices, of whichthe following is a full, clear, and exact description.

My invention relates to improvements in tuning devices, and it consistsin the combinations, constructions, and arrangements herein describedand claimed.

An object of my invention is to provide a device of the characterdescribed in which means is provided for comparing the frequency ofvibration of a standard tuning fork and a piano string to determinewhether or not the piano string is in tune.

Another object of my invention is to pro vide a device of the characterdescribed which does not rely upon a comparison of audible waves as theordinary tuning done by ear, `but instead, by the comparison ofmechanically reproduced pulsating electric current. Y

A further object of my invention is to provide a device of the'characterdescribed which may be used to advantage where more than one instrumentis tuned in the same room and audible tuning would occur.

Another object of my invention is to provide a device of the characterdescribed which is compact in form, which is easy to operate, and whichis thoroughly practical commercially.

Other objects and advantages will appear in the following specificationand the novel features of the invention will be particularly pointed outin the appended claims.

My invent-ion is illustrated in the accompanying drawings` forming partof this application, in which Figure 1 is a side elevation of one of thestandard timing forks and a portion of the mechanism for operating thefork,

Figure 2 is a top plan view of the mechanism illustrated in Figure 1,

Figure 3 is a diagrammatic view of the electrical connections of aportion of the, tuning device,

Figure 4 is a sectional view of a portion of the tuning device,

Figure 5 is a sectional view along the line 5 5 of Figure 4,

Figure 6 is a diagrammatic view of the DEVICE.

8, 1822. Serial No. 586,906.

eletrical connections of the tuning device, an

Figure 7 is a side elevation of a modilied form of the mechanismillustrated in Figures 4 and 6.

In carrying out my invention, I make use of a plurality of tuningforks 1. I provide one tuning fork for each yof the cords or strings ofthe instrument to be tuned, and the forks each produce a sound wave thatmay be a standard. I have shown only one of the forks and the mechanismfor operating the fork for the purpose of simplicit The fork 1 ismounted upon a suitable base as shown. A pair of split ring magnet cores2 and 3 are mounted adjacent to the upper ends 4 of the fork 1 so that:the ends 4 of the fork may lie slightly in front of the gap 5 betweenthe adjacent ends of the cores 2 and 3. Each of the cores 2 and 3 isprovided with a magnet winding 6 and 7 respectively. The terminals 8 and9 of the magnet winding 6, and the terminals 10 and 11 of the magnetwinding 7 are connected by means of a jack 12 to the ordinary type ofswitch board plug 13 having four lead wires, one for each of theterminals 8 to 11 inclusive. The broken line 14 in Figure 3 representsthe relative position of the jack and plug 12-13 in the circuit.

A vacuum valve 15 of the ordinary type having a filament 16, a plate 17and a grid 18 is provided and secured on a suitable mounting, togetherwith a B battery 19 for the plate circuit, and a filament battery 20. Indescribing the electrical connect-ions for this portion of the device, Ishall consider that the plug 13 is inserted in the jack 12 and thereforedescribe the completed circuit. The filament battery 20 is connected inthe usual manner by feed wires 2l and 22 to the filament 16. The pluspole of the B battery 19` is connected to the plate 1T and the negativepole of the battery 19 is connected to the terminal 8 of the magnetwinding 6. The terminals 9 and 10 of the magnet windings 6 and 7 areconnected to one another at 23 and to the filament circuit 20, 21, and22 between the battery and filament by a connector 24. The terminal 11of the magnet winding 7 vis connected to the grid 18 of the valve 15.The mechanism and circuit described above constitutes the mechanism forgenerating a pulsating current having a frequency that is perfectlysynchronized with the natural eriod of vibration of the tuning fork 1.

he operation thereof will be hereinafter described.

A transformer which I choose to call a differential transformer, isprovided, and is constructed of a closed core 26 having three branches27, 28, and 29. The three branches 27 to 29 inclusive, are provided withwindings 30 to 32 respectively, the winding 31 being on the intermediateor central branch 28. The terminals 33 and 34 of the windin 32 areshunted across the plate circuit o the generator at 23 and at thenegative pole of the battery 19 by means of connectors 35 and 36,respectively. This connection therefore permits a portion of the currentin the secondary or plate circuit of the valve 15 to flow through thecoil 32.

The means for generating a pulsating current having a frequencysynchronous with the period of vibration of the piano cord or string asshown at 37 on the piano sound pole 30 is provided as follows. A shellof iron 39 is supported upon the supporting arm 40 and is provided witha handle 41 for guiding the movement thereof. The supporting arm 40forms a portion of a carriage 42 having a roller 43 which may be movedlongitudinally of the piano sound board 38 so that the shell 39 may bebrought into registration with any of the various cords or strings ofthe piano. The shell 39 is provided with a pair of compartments 44 and45, each having a restricted opening 46 and 47, respectively, at theforward end of the shell 39.` Round iron core pieces 48 and 49 arecentrally located in the compartments 44 and 45, respectively, andarranged to project through the restricted openings 46 and 47.

A pair of magnet coils 50 and 51 are disposed in the compartments 44 and45 concentric the cores 48 and 49. The coils 50 and 51 are connected inseries with one another and are provided with terminals 52 and 53 whichterminals are connected by means of a feed cable 54 to a low voltagebattery (not shown) which may be, if desired, the filament battery 20.When cur rent is flowing through the coils 50 and 51, a strong magneticlinx is built up about the cores and the outer ends of the core pieces48 and 49 form one pole of the magnet, and

the forward end of the shell 39 forms the opposite pole, so that astrong field is built up on the annular space between the restrictedopenings 46 and 47 and their respective pole pieces 48 and 49.

A delicately constructed lever 55 is pivotally mounted intermediate itslength, as shown at 56, upon the shell 39, one portion 57 of the leverextending downwardly below the lower side of the shell 39 and bentlaterally adjacent to its end at 58 so that the tip 59 thereof, which isslightly enlarged, may rest upon the cord or string 37 of the piano. Apair of armature coils 60 and 61 are supported upon either side of thepivotal point 56 so that the coil 60 may lie in the space intermediatethe opening 46 in the pole 48, and the coil 61 ma lie in the spacebetween the opening 47 1n the pole piece 49. It will be apparent at thistime that movement of the lever 55 as by vibration of the string 37 willcause simultaneous movement of the coils 60 and 61. If current isflowing through the ma et coils 50 and 51, the coils 60 and 61 wil cutthe magnetic field previously described and the current will begenerated therein.

The connections for this portion of the mechanism are clearly shown inFigure 6 and consist in a vacuum valve 62 identical to the valve 15. A Bor plate battery 63 is connected with its positive pole and joined by aline 64 to the plate 65. The negative pole of the battery 63 isconnected by means of a line 66 to one terminal of the coil 61 and toone terminal of the winding 30 upon the transformer 25. The otherterminal of the coil 61 is connected by means of a line 67 to thefilament intermediate the lament battery 68 and the filament 69 and alsoto one terminal of the coil 60. The opposite terminal of the coil 60 isconnected by means of a wire 70 to the grid 71 of the vacuum valve 62. Aline 72 connects the line 67 to the opposite terminal of the coil 30 ofthe transformer 25. The coil 31 of the transformer 25 is connected withone of its terminals 73 to one post 74 of a galvanometer 75. Theopposite terminal of the coil 31 is connected by means of a line 76 tothe remaining post 77 of the galvanometer 75. A pair of head phones 78are shunted across the terminal 73 in the line 76, i. e., across thegalvanometer 75.

From the foregoing description of the various parts of the device, theoperation thereof may be readily understood. Let us assume that the Gstring of the piano is out of tune. The operator would first insert theplug 13 into the jack 12 adjacent the fork 1, which fork was constructedto produce a wave having theperiod of Vibration of the'true G. It shouldbe understood that in this device there are a plurality of the forks,one for each of the strings, and that the connections with the plug 12are the same in each of the forks, i. e., each of the forks is providedwith a magnet 6 and 7, and cores 2 and 3.

It is understood by those experienced in the handling of vacuum tubecircuits that the proper normal negative potential is maintained on thegrid 18 by an adjustable resistance shunted across the filament battery20 so as to operate the tube on the desired portion of itscharacteristic curve which in this case will be the center of thestraight portion, thereb allowing a fixed amount of current to owthrough the windings 6 and 32 from the B battery 19 contained in theplate circuit of the valve 15, this current will flow all the time thelug 13 is in position and the prong 81 of t e fork 1 is at rest.

As the plug 13 is inserted in the jack 12, the filament 16 of the valve15 which is already incandescent, will )ermit a flow of current from theplate 1l to the filament and this current will flow through the magnetwinding 6 in its course from the plug terminal of the battery 19 to thenegative terminal. T he property of the vacuum valve to conduct currentfrom the plate to the filament is a well established fact. The plug 13in feeding the jack, makes a connection very quickly and as currentflows through the magnet 6, the leg 80 of the fork 1 will be drawntoward the end of the walls of the core 2.

This will cause the opposite leg or prong 8l of the fork 1 to movetowards the walls 5 of the core 3. It should be here noted that the core3 possesses a slight residual magnetism.

Movement of the prong 81 towards the end of the walls 5 of the core 3will cause a change in the flux through the coil 7, and a feeble currentwill be induced in the coil 7. Since the coil 7 is in series with thefilament and the grid of the valve 15, the movement of the prong 81towards the coil 7 will cause the grid 18 to receive a slight positivecharge, whereupon the flow of current in the magnet 6 will increase(another well established property of the vacuum valve). As current inthe plate circuit which includes the coil 6 is increased, the magneticfield about the core 2 will attract the prong 80 still further whichwill also cause the prong 81 to move still further towards the magnet 7,malting'tlie grid more positive, increasing the flow of current throughthe magnet 6 still more which attracts the prong 80 further. This actiontakes place until the prongs 8() and 8l reach their outward limit ot`vibration.

.\s the prong 81 reaches its limit of vibration. thereby coming to arest, the.. generation of current in the coil 7 ceases, the positivecharge that wasl on the grid 18 now falls to normal which is slightlynegative` due to the inherent actionv of the valve. The cui'- rentfiowing through the plate circuit and the coil 6 decreases to normallowering the magnetic field about the prong 80, which released itsomewhat letting it move back away from the coil G; the prong 81 therefore also moves away from the coil 7 which generates a current in tbecoil 7 in they opposite direction to the last; the grid already having anegative charge (normal) is now made moi'e negative by the increasedflow of current from the filament 16 to the grid 18 from the coil 7 thecurrent through the plate circuit and coil 6 decreases still more,releasing the prong 80 from the magnetic field almost entirely and itmoves to its limit of vibration inward, the prong 81 alsomovcs inward toits limit of vibration. The prongs S0 and 81 tending to move back totheir normal position, starts the second cycle of its oscillatory orvibratory movements. lt can he readily seen at this time that as thefork is moving to one extent of its oscillatory or vibratory paths, thegrid will he charged either negative or positive and the plate currentdecreases or increases, thus maintaining the fork 1 in constantribrations of equal amplitude and thc 'plate circuit will have apulsatin r direct current flowing therethrough, wliic i current willhave a frequency that is perfectly synchronized with the movements ofthe fork 1.

We will assume therefore that the fork 1 is in operation and that thefrequency of the current in the plate circuit, of which a small amountis owin through the coil 32 of the transformer 25,!iias a frequency thatis synchronous with the standard musical tone The operator will thenmove the shell 39 by means of the handle 41, so that the enlarged ti 59of the lever 55 will contact the G cord)37 of the piano, which cord isto be adjusted and tuned.

As the operator touches the string 37 with the tip portion 59, thecontact therewith will set the string into vibration, and the lever willvibrate with the cord. As the lever 55 vibrates, the coil 60 supportedthereon will move in the magnetic field heretofore described between theopening 46 and the core piece 48. This movement will generate acurrentin the coil 60, one terminal of which is connected to thefilament 69 by means of the connector 67, and the other terminal to thegrid 71. The grid 71 will thereupon receive alternately positive andnegative charges and the current which is normally flowing from theplate 65 to the filament 69 when the coil 6() is at rest, will either beincreased or decreased in the coil 6l, thereupon forcing the string 37inward or permitting the string to more outward following in contactwith the tip 59; owing to the vibration of the string 37 and the gradualincrease and relaxation of the tension against the string 37 by thelever 55 the coil 60 will oscillate in the magnetic field vgenerating asmooth alternating current .wave therein. The coil G1 will receiveinstantaneously a pulsating direct current of the identical wave forni,although of greater amplitude which keeps the string 37 in constantvibrations of equal amplitude.

The normal flow of current through the plate circuit and coil 61 whilethe coil 60 is at rest, would tend to keep the coil 6l at its outwardlimit of movement, but when the tip is pushed against the string 37, thecoil 6i is forced back to the center of the magnetic field` rlherefore apulsating direct current in the coil 61 will cause a. relaxaf ion orincrease of tension on the string, causing a smooth to and fro movementof the coils and (il, string 37, and lever 55. ..\s the current flowsthrough the coil 6l, the coil 6l and the electromagnet 5l wouldvirtually constitute a motor which would serve to force a movement ofthe .lever 55. The` current in the coil 6l would cease when the leverhad moved to the opposite end of its oscillatory movement and theoperation heretofore described would repeat itself, so that it may bereadily seen that the lever 55 would be propelled in an oscillatorymovement upon its pivotal point 56 with a frequency synchronous with theunadjusted or untuned frequency of the string or cord 37.

A portion of the current from the central or plate circuit of thisportion of the device is arranged to flow through the coil 3() of thetransformer 25, and therefore the frequency of pulsations of thiscurrent would also be p-resent in the coil 30.

It has been found that where a trans? former of the character shown at25 has been used, and the end branches provided with coils in whichcurrent of different frequencies are passed, that the difference betweenthe frequency of the pulsations of the current is registered in aninduced current in a coil, such as the coil 31 upon the intermediate orcentral branch. The operator therefore observes the galvanometer 75 andif the indicating hand oscillates, he has knowledge that there is adifference in the frequenc i of the current in the plate circuit of tlievalve 16 and the plate circuit of the valve 62 and therefore the string37 is not tuned with the fork 1. If this difference is so great, i. e.,more than could be registered b use of the galvanometer 75, then the dierence may be observed by use of the phones 78 which will buzz. Theoperator thereupon adjusts the string 37 until the galvanometer showssome movement. IIe can then complete the.adjustment by watching thegalvanometer and when the needle does not move but stands perfectlystill, the string 37 is in tune with the fork l and the plate circuitsof the valves 16 and 62 each have pulsating current of identicalfrequencies.

In Figure 7 I have shown a modified form of the mechanism illustrated inFig ure 6, in which in place of using the vacuum valveand the mechanismshown in Figures 4 and 5, I employ the ordinary type of telephonetransmitter 8la and a battery 82 in series therewith. One terminal 83 ofthe battery of the oppositev pole and transmitter 8l, as shown at 84, isconnected directly to the coil 30 of the transformer 25. This modifiedform of the device is particularly well adapted for organs, and it wouldbe impossible to use the device shown in Figure 4 for this purpose. Theoperation of the modified form 1s quite simple in that as the Wavesstrike the transmitter 8l, a pulsating current is permitted to flowthrough the coil 30 simply because the resistance of the transmitterincreases and' decreases as the waves strike the transmitter and thefrequency of these waves may be compared in precisely the same manner asthe frequency of the current in the plate circuit of the valve 62 of thetuning fork l.

I claim:

1. A tuning device of the character described comprising a differentialtransformer having three windings thereon, means for generating apulsating current having a predetermined frequency, said current beingdirected through one of the windings on said transformer, means forproducing a pulsating current having an uncertain frequency, said lastnamed current being directed to flow through the second winding on saidtransformer, and means electrically connected with the third Windino onsaid transformer for detecting any di erence in frequency between thecurrent of predetermined and uncertain frequency.

2. A tuning device of the character described comprising a differentialtransformer having three windings thereon, means for generating apulsating current having a predetermined frequency, said current. beingdirected through one of the windings in said transformer, means forproducing a pulsating current having an uncertain frequency, said lastnamed current being diw rected to fiow through the Second winding onsaid transformer, and a galvanometer connected with the third winding onsaid transformer whereby any difference in frequency between the currentof predetermined and uncertain frequency may be visually indicated.

A tuning device of the character described comprising a differentialtransformer having three windings thereon, means for generating apulsating current having a predetermined frequency, said current beingdirected through one of the windings in said transformer, means forproducing a pulsating current having an uncertain frequency, said lastnamed current being directed to flow through the second winding on saidtransformer, and a telephone receiving mechanism connected with thethird winding on said transformer whereby any difference in frequencybetween the current of predetermined and uncertain frequency may beaudibly indicated.

4. In a device of the character described, a vacuum valve having a platebattery, a filament battery, a plate circuit, and a grid circuit, alever pivotally mounted intermediate its length and adapted forengagement with the string of a piano or the like, a pair of armaturecoils on said lever, and means for maintaining the electromagnetic fieldabout said armature coils, one of said armature coils being connected inseries with said plate circuit and the other being connected in serieswith said grid circuit.

5. -In a device of the character described, an electromagnetic fieldunit, a lever pivotally mounted intermediate its length on said fieldunit, a pair of armature coils in operative registration with the polesof said field piece, said lever being provided with a laterally bentportion fashioned to engage the string of a piano or the like, andelectrically operated means associated with said armature coils formaintaining said lever in oscillatory motion on its pivotal support at afrequenc synchronous with the natural period of v1 ration of said pianostring when said lever is placed in engagement with said string.

6. In a device of the character described, I

a tuning fork, a pair of electromagnets, one in registration with eachof the prongs of said tuning fork, a vacuum valve having a platebattery, a filament batter a plate circuit, and a grid circuit, one osaid electric magnets being connected in series with said late circuit,and the other of said magnets eing connected in series with said gridcircuit, whereby said tuning fork may be kept in constant vibration andthe plate circuit may carry a pulsating current having a frequencysynchronous with the frequency (fit 1tihe sound waves emitted by thetuning 7. A tuning device of the character described comprising meansfor generating a ulsating current having a predetermined requencysynchronous with a known audible vibration, means for generating apulsating current having a frequency synchro nous with an unknownaudible vibration, and electrical means associated with said first andlast named means for detecting any difference in frequency in thecurrent of known frequency and the current of unknown frequency.

LUCIEN J. BEINDORF.

